Ambient PM10 and PM2.5 were intensively sampled at two sites in the air basin of southern Taiwan during the periods of 14-21October 2003, 2-9 January and 26 Febuary-4 March 2004 respectively. High values of PM2.5/PM10 ratio were observed on the occasions of high PM10 levels. Therefore, to understand the formation mechanism and source apportionments of ambient PM2.5 is a key to develop PM10 control strategies. According to the backward trajectory calculated from MM5 during high PM2.5 levels, it suggests that air currents should bring air pollutants from western urban areas to the air basin of southern Taiwan and there were relatively weak wind zones which were adverse for diffusion of air pollutants. The accumulation of imported and local generated suspended particulates led to unhealthful air quality in the air basin. The CMB receptor model was used to estimate source contributions. Major contributors to PM10 were geological material and secondary pollutant species. Pollution sources of PM2.5 tended to be dominated by secondary species, vegetative burning, vehicle exhaust and coal combustion. The contributions of nitrates obviously increased during high measurements of PM10. It is recommended that the stricter control and monitoring programs for NOX and NH3, the precursor of nitrates, should be implemented in western and southern Taiwan especially during the periods of high PM10 levels. According to the information on enforcement costs and reductions of suspended particulates provided by the local Environmental Protection Bureaus in southern Taiwan, it was observed that the strategies on prevention of PM10 for construction projects demonstrated its unique benefits with higher reductions and lower unit cost. Nevertheless, secondary pollutant species were not reported by the information. Since the major pollutant sources of NOX, the precursor of nitrates, are plants and vehicles, we suggest establishing strategies on reduction of stationary and mobile sources with the concepts of multimedia enforcement and green transportation.

the air basin of southern Taiwan,suspended particulates,MM5 modeling,backward trajectory,receptor model,control strategies,